There's already the map classBTypeFromInternalNameMap in BTypes which
stores all ClassBTypes.

Introduces methods for textifying classes, methods, InsnLists and
individual AbstractInsnNodes.

This infrastructure is required for the inliner: when inlining code
from a classfile, the corresponding ClassBType is needed for various
things (eg access checks, InnerClass attribute).

The test creates two ClassBTypes for the same class: once using the
(unpickled) Symbol, once using the parsed ASM ClassNode, and verifies
that the two are the same.

There's a cleanup to the InnerClass attribute:

    object T { class Member; def foo = { class Local } }
    class T

For Java compatibility the InnerClass entry for Member says the class
is nested in T (not in the module class T$). We now make sure to add
that entry only to T, not to T$ (unless Member is actually referenced
in the classfile T$, in that case it will be added, as required).